Amorphous nylon copolymer and copolyamide films and blends

ABSTRACT

Novel orientable single and multilayer thermoplastic flexible films utilizing blends comprising an amorphous nylon copolymer such as nylon 6I/6T and a nylon copolyamide having a melting point of at least about 145° C. having improved processability, shrinkage and optical properties.

This application is a division of prior U.S. application Ser. No.07/685,950, filed on Apr. 16, 1991 now U.S. Pat. No. 5,344,679 which isa division of application Ser. No. 07/235,258 filed on Aug. 23, 1988 nowU.S. Pat. No. 5,053,259.

BACKGROUND OF THE INVENTION

The present invention relates to nylon resin blends, single andmultilayer films and casings containing nylon resin blends for use inpackaging. In particular, the invention relates to nylon blends, filmsand casings and/or bags made thereof which are suitable for packagingfood products such as fresh meat, processed meat, cheese and sausages.

Nylon is the generic name for a family of polyamide polymerscharacterized by the presence of the amide group-CONH. The utility ofnylon compositions and products are well known with everyday examplesincluding usage in packaging, brushes, and tires, as synthetic films,fibers, plastics and molding resins.

Thermoplastic flexible films are used in a wide variety of applicationsincluding bags (e.g. for merchandise, leaves, garbage) wrappings forindustrial packaging, in electrical and electronic uses, ascommunications media substrates, adhesive coated products such as tapesand labels, medical packaging, and food packaging.

In the food industry, thermoplastic flexible films are used to keep foodfresh prior to consumption. Greater use of centralized processing offoods in conjunction with increased handling and longer delivery timesassociated with long distance transportation have increased the demandfor packaging films having superior properties.

In the poultry and meat segments of the food industry thermoplasticflexible films are utilized to maintain freshness. Meat is frequentlysold fresh, frozen or cooked; therefore films advantageously provideprotection at various temperatures. Food items such as primal andsubprimal cuts of beef, ground beef and processed meats are known to usecoextruded or laminated films which utilize such compositions as nylon,polyester, copolymer of vinylidene chloride (PVDC), ethylene-vinylacetate copolymer (EVA) and ionomers.

It is also generally known that selection of films for packaging foodproducts includes consideration of such criteria as barrier properties,cost, durability, puncture resistance, flex-crack resistance, FDAapproval, machinability, optical properties such as gloss and haze,printability, sealability, shrinkability, shrink force, stiffness, andstrength.

In general, nylon films are made by processes which include casting orblown film and these films may be uni- or biaxially oriented. Specifictypes of nylon such as nylon 6, nylon 6,6, and nylon 12 have been madeinto films. Known advantages of nylon films relative to other filmmaterials in packaging applications include good oxygen and flavorbarrier characteristics, durability at low temperatures and thermalstability. However, nylons in general are costly and are poor moisturebarriers. It is known to use certain nylon films as core layers inoriented multilayer films. However, nylon selection is critical andprocessing is very difficult. These multilayer films may include one ormore additional layers of films made of various resins, for example, lowdensity polyethylene (LDPE), ethylene-vinyl acetate copolymer (EVA),ionomer, PVDC, or copolymers of ethylene and methacrylate. Nyloncontaining films have also been used in vacuum packaging of fresh meat.Typical and generally known films suitable for packaging and informationon film manufacture are described in the Encyclopedia of Polymer Scienceand Engineering 2nd Ed., Vol. 7, pp. 73-127, Vol. 10, pp. 684-695 (JohnWiley & Sons, Inc., 1987) whose teachings are hereby incorporated byreference.

Also, amorphous nylons have been disclosed as useful in thermoplasticfilms including multilayer films and biaxially drawn films.

U.S. Pat. No. 4,698,195 and European Patent application No. 240,632 bothdisclose a process for preparation of a biaxially drawn polyamide filmwhich utilizes what is termed "a substantially amorphous unorientedpolyamide film".

Also, U.S. Pat. No. 4,668,571 (Moriarty, Jr.) discloses a multilayerstock material useful for producing flexible, thermoplastic bags inwhich an outer layer may comprise a polyamide resin. Among the examplesof suitable polyamide resins is listed amorphous nylon.

Additionally, European Patent application No. 236,099 (Fantet al)discloses a multilayer thermoplastic film having optional polyamidelayers. Suitable polyamides are said to include a commercially availablecopolymer of nylon 6 and nylon 12 having a composition of about 60%nylon 6 and about 40% nylon 12 by weight sold under the trademark GrilonCA-6 by Emser Industries. Another suitable nylon copolymer is disclosedas CR-9, having 20% to 30% nylon 6 and 70% to 80% nylon 12 by weight.

Also, more recently coextruded film packaging for processed meat wasreportedly being used in Japan which utilizes an amorphous nylon soldunder the brand name Novamid X21 by Mitsubishi Chemical Industries Ltd.of Tokyo (See "Coextrusion Developments Focus on Barrier Resins",Plastics Technology, Vol. 33, No. 13, pp. 5, 77-79, December. 1987 BillCommunications, Inc., New York).

Oriented nylon films are also well known in the packaging industry fortheir toughness, puncture resistance, and oxygen barrier properties. Inparticular, biaxial orientation is known to generally improve filmstrength. The oxygen barrier properties of oriented nylon filmsgenerally provide greater resistance to oxygen permeability as the levelof absorbed moisture decreases. As the moisture content increases, theoxygen barrier properties of most oriented nylons deteriorate. Whennylon films are to be used or stored under humid or other moistconditions, it becomes desirable to protect the nylon film e.g. byplacement between layers having relatively low permeability to moisture,in order to keep the nylon dry. However, orientation of coextrudedmultilayer blown films having nylon as a protected core layer isdifficult due to processing constraints. Often nylon is the outer layerin coextruded processing because of the necessity for rapid quenching toachieve suitable processing in a multilayer structure. Of course,lamination processes may be and are presently utilized to attach amoisture protective layer to nylon, but this is disadvantageouslyexpensive.

In many packaging applications, it is also desirable that at least oneof the layers have good heat seal properties. Resins which have bothgood heat sealability and are substantially impermeable to moistureinclude various polyethylenes, ethylene copolymers and ionomers.Oriented nylon films are currently used alone and in combination withthese heat sealable and moisture resistant layers.

Disadvantageously, it has proved difficult to find film layers (otherthan PVDC) which have good barrier properties to both moisture vapor andoxygen. Therefore, multilayer films are commonly employed to utilize themost beneficial properties of various film layers.

The Encyclopedia of Polymer Science and Engineering, 2nd Edition., Vol.7, pp. 77-79 (John Wiley & Sons, Inc., 1987) discloses that "nylon isfrequently the core portion of the film being coextruded or coated withsealant resins, such as LDPE, EVA, ionomers, or copolymers of ethyleneand methacrylate". The nylon layer acts as an oxygen and flavor barrierfor such applications as processed meat and cheese packaging,boil-in-bags, and bags for baked goods.

In a typical known process for producing multilayer films containingoriented nylon, the nylon film is oriented by heating to a softenedstate below the melting point and stretching the softened material. Manyconventional nylon resins crystallize very rapidly and have meltingpoints well in excess of adjacent polyethylene layers. Due to thesetemperature differences and because nylon and polyethylene tend to havedifferent stretching characteristics, the nylon layer is typicallyoriented separately and in advance of its combination with the adjacentpolyethylene layers. The combination of the oriented nylon with theadjacent layers is then accomplished using a conventional but relativelyexpensive and complex lamination process. This requires an adhesive suchas polyurethane type adhesive applied with a coater-laminator.

Another problem with current multilayer oriented nylon structures isthat, while a material such as polyethylene generally protects the nylonfrom moisture, some moisture gradually seeps in from either the packagedfood article or the atmosphere and is absorbed by the nylon. This causesan increase in oxygen permeability which shortens the shelf life ofoxygen sensitive foods.

Due to recent growth in the market for barrier films, there currentlyexists an industry wide search for films with improved barrierproperties such as low oxygen permeability and low water permeability.For economic reasons, there is also a demand for an oriented nylonmultilayer film which can be produced by a coextrusion process.Production of multilayer films by coextrusion is generally moreeconomical than use of lamination methods.

The present invention provides an improved nylon resin blend and singleand multilayer films thereof which ameliorate many problems associatedwith known films.

It is not necessary that each and every problem listed above be overcomeby all embodiments of the invention. It is sufficient that the inventionmay be advantageously employed when compared to the prior art.

SUMMARY OF THE INVENTION

According to the present invention a novel nylon or polyamide resinblend of an amorphous nylon copolymer and a copolyamide having a meltingpoint of at least 145° C. is disclosed. This newly disclosed blend maybe utilized to form novel thermoplastic flexible films of one or morelayers. These inventive films are surprisingly easy to process andorient. For example, the blends of the invention form films which arerelatively easy to biorient compared to films of the individual blendcomponents alone. In particular, many crystalline nylons exist which areknown to be extremely difficult to biaxially stretch in order to formshrinkable films. It has been presently discovered that blends of theseorientation-resistant nylons with an amorphous nylon copolymer nylon6I,6T produces a film which may be easily uniaxially or biaxiallyoriented. For example, biorientation of a film layer formed of nylon6/12 alone is very difficult and attempts at biorientation are oftenunsuccessful. However, a blend of nylon 6/12 with an amorphous nylon maybe easily uniaxially or biaxially oriented according to the presentinvention. Surprisingly, the present invention shows successful biaxialorientation of either single layer film, or coextruded multilayer filmshaving a nylon containing intermediate layer, wherein the nylon layercomprises a blend of a nylon copolyamide having a melting point of atleast 145° C. with an amorphous nylon. These films have excellentoptical and oxygen barrier properties.

According to the present invention the entire multilayer film isbiaxially stretched without the necessity for separately biaxiallystretching the nylon containing layer independent from the non-nylonlayers followed by lamination of the individual stretched layers.

Unexpectedly, addition of an amorphous polyamide such as nylon 6I/6Thaving a glass transition point of about 127° C. to a copolyamide suchas nylon 6/12 forms a blend which may be easily processed into ashrinkable film. This film exhibits high gloss and low haze and goodshrinkage values at temperatures well below 127° C. Addition ofamorphous nylon to nonamorphous copolyamides according to the presentinvention results in great improvements in one or more of suchproperties as haze, gloss, oxygen permeability, tensile strength,dynamic puncture or shrink percentage after extrusion.

Also, unexpectedly it has been discovered that addition to the aboveinventive blends of a homopolymer such as nylon 11 having a relativelyhigh O₂ permeability value actually lowers O₂ permeability of theresulting film. Advantageously, blends of the present invention may beemployed to form uniaxially or biaxially oriented single or multilayerfilms by a variety of orientation processes.

DETAILED DESCRIPTION OF THE INVENTION

Polyamides include nylon resins which are well known polymers having amultitude of uses including utility as packaging films, bags and casing.See, e.g. Modern Plastics Encyclopedia, 88 Vol. 64, No. 10A, pp 34-37and 554-555 (McGraw-Hill, Inc., 1987) which is hereby incorporated byreference. In particular, the novel blends, thermoplastic flexiblefilms, and oriented multilayer films of the present invention are usefulin food packaging.

The invention utilizes an amorphous nylon copolymer as a component of anovel resin blend used to produce novel single and multilayer films. Theterm "amorphous" as used herein denotes an absence of a regularthree-dimensional arrangement of molecules or subunits of moleculesextending over distances which are large relative to atomic dimensions.However, regularity of structure may exist on a local scale. See,"Amorphous Polymers," Encyclopedia of Polymer Science and Engineering,2nd Ed., pp. 789-842 (J. Wiley & Sons, Inc. 1985). In particular, theterm "amorphous nylon copolymer" as used with respect to the presentinvention refers to a material recognized by one skilled in the art ofdifferential scanning calorimetry (DSC) as having no measurable meltingpoint (less than 0.5 cal/g) or no heat of fusion as measured by DSCusing ASTM 3417-83.

Suitable amorphous nylon copolymers includehexamethyleneisophthalamide-hexamethylene terephthalamide copolymer alsoreferred to as nylon 6I/6T. A preferred component of the invention ishexamethyleneisothalamide-hexamethylene terephathalamide copolymer whichhas from about 65 percent to about 80 percent of its polymer unitsderived from hexamethyleneisophthalamide. Especially preferred as theamorphous nylon copolymer component is a commercially available nylon6I/6T sold by the DuPont Company of Wilmington, Del., U.S.A. under thetrademarked designation Selar PA 3426.

Selar PA 3426 is further characterized by DuPont Company technicalbulletin E-73974 dated 12/85, which is hereby incorporated by reference,as an amorphous nylon (polyamide) having superior transparency, goodbarrier properties to gases such as O₂, solvents and essential oils andalso the following properties according to the indicated standards:density of 1.19 gm/cc (ASTM D1505): glass transition temperature of 127°C. (ASTM D3418): heat deflection temperature of 126° C. at 4.6 Kg/cm²(66 psi) and 123° C. at 18.4 Kg/cm² (264 psi) (ASTM D648), and flexuralmodulus of 27,900 Kg/cm² (400,000 psi) at 50 percent relative humidityand 23° C. (ASTM D790).

The amorphous nylon copolymer used in the present invention may bemanufactured by the condensation of hexamethylenediamine, terephthalicacid, and isophthalic acid according to known processes. It is preferredthat a nylon 6I/6T resin be used which is manufactured such that 65 to80 percent of the polymer units are derived from hexamethyleneisophthalamide. Advantageously, such resins (which are furthercharacterized as having a specific gravity of 1.207±0.1, no meltingpoint, and having the solubility and extraction values listed in TableI) have been approved for food contact in the United States by the Foodand Drug Administration. (See 52 Fed. Reg. 26,666-26,667, Jul. 16, 1987,the disclosures of which are hereby incorporated by reference).

                  TABLE 1                                                         ______________________________________                                                      Maximum extractable fraction                                                  as selected solvents                                            Solubility in (% by weight of resin)                                          Nylon boiling              95% Ethyl                                                                             Ethyl  Ben-                                resin 4,2N HCl    WATER    Alcohol Acetate                                                                              zene                                ______________________________________                                        Nylon Insoluble after                                                                           0.2      1.0     0.1    0.1                                 6I/6T 1 hour                                                                  ______________________________________                                    

Suitable copolyamides useful in forming the blends and films of thepresent invention are copolyamides having a melting point of at least145° C. A suitable method of determining a melting point is by usingdifferential scanning calorimetry as above to determine the heat offusion. Preferred copolyamides melt at temperatures within a range offrom about 145° C. to about 215° C. Copolyamides with melting points inthis range have been found to form useful blends with the above notedamorphous nylon copolymers, which blends are easy to process into filmsincluding oriented films. In film packaging applications, copolyamideswith melting points less than 145° C. soften and distort at typicalprocessing temperatures which include e.g. 82°-93° C. (180°-200° F.) forshrink wrapping and 71°-82° C. (160°-180° F.) for cooking sausages.Copolyamides especially suited as components of the inventive films andblends are copolyamides which comprise a copolymer of nylon 6 with atleast one other polyamide whereby the copolyamide has a melting point ofat least about 145° C. Preferably, these especially suited copolyamideshave a melting point less than about 215° C. Mixtures of copolyamidesare also contemplated.

Preferred copolyamides are nylon 6/12 and nylon 6/66 and mixturesthereof. Nylon 6/12 and nylon 6/66 copolyamides are commerciallyavailable. For example a nylon 6/12 copolyamide which melts within arange of from about 195°-200° C. (ASTM D2117) is commercially availableunder the trademark Grilon CR 9 from Emser Industries of Sumter, S.C., adivision of EMS-American Grilon, Inc. (EMS).

Mixtures of copolyamides may be usefully employed in the presentinvention. For example, two or more copolyamides each having a meltingpoint of at least 145° C. may be used, or a copolyamide having a meltingpoint of at least 145° C. may be mixed with one or more othercopolyamides which have melting points less than 145° C. or areamorphous themselves. A suitable copolyamide for mixing which has amelting point less than 145° C. is another nylon 6/12 copolyamide whichmelts at about 134° C. (DSC max.) which is commercially available fromEMS under the trademark Grilon W6220. In an especially preferredembodiment of the invention, mixtures of these two nylon 6/12copolyamides are utilized. A copolyamide of nylon 6/66 which melts atabout 195° C. is commercially available from Allied-Signal under thetrademark Nylon 1539, mixtures of one or more nylon 6/12 copolyamideswith one or more nylon 6/66 copolyamides may be usefully employed in theinvention. Also, mixtures of various nylon 6/12 compositions may beemployed to optimize properties. Advantageously, a most preferred nylon6/12 copolyamide mixture may be formed from about 80 percent by weightof Grilon CR9 and 20 percent by weight of Grilon W6220.

In addition to the first component of an amorphous; nylon copolymer andthe second component of a copolyamide having a melting point of at least145° C., the blends and/or films of the present invention may alsoemploy as a third component a polyamide homopolymer. It has been foundthat a nylon homopolymer may be added to decrease gas permeability andthereby improve the gas barrier properties of the blend. Suitablehomopolymers include such commercially available nylons as nylon 6,nylon 11 and nylon 12.

According to the present invention, a nylon resin blend is providedcomprising, as a first component of the blend, an amorphous nyloncopolymer and, as a second component, a polyamide having a melting pointof at least 145° C. The first component is preferably nylon 6I/6T whichis an amorphous hexamethyleneisophthalamide-hexamethyleneterephthalamidecopolymer. Advantageously, a nylon 6I/6T having from about 65 to about80 percent of its polymer units derived from hexamethyleneisophthalamidewill be employed with a commercially available composition sold underthe brand name Selar PA 3426 by the Dupont Company of Wilmington, Del.being especially preferred. The second component is preferably a nylon6/12 alone or a mixture of nylon 6/12's. Advantageously, a mixture of(i) a nylon 6/12 having a melting point between about 145° C. and 215°C. with (ii) a nylon 6/12 having a melting point of less than about 145°C. is employed. Especially preferred is a mixture of about 80% by weightof a nylon 6/12 known as Grilon CR9 and about 20% by weight of a nylon6/12 known as Grilon W6220, both nylon 6/12 copolyamides being sold byEmser Industries of Sumner, S.C.

Optionally, a third component may be advantageously employed. As notedabove, a homopolymer such as nylon 6, nylon 11, or nylon 12 may be addedas a third component to the blend. Surprisingly, addition of a preferredhomopolymer such as nylon 11 increases the barrier properties of thefilms of the blend to transmission of oxygen gas. A fourth component ormore such as other nylon copolymers (e.g. nylon 6/66), or otheramorphous nylons may also be added to the blend.

Unless otherwise specified, all weight percentages herein are based uponthe total weight of the resin blend.

Advantageously, the first component (amorphous nylon copolymer) will bepresent in an amount of from about 10 to about 70 weight percent. Use ofamounts less than 10 wt. % reduces the beneficial effect of enhancedproperties attributable to the amorphous nylon copolymer component. Inparticular, the haze of films increases noticeably at lower amounts.Also, use of amounts greater than 70 wt. %, has a deleterious effect onprocessability, particularly with respect to producing biaxiallyoriented single layer films. Bubble formation becomes increasinglydifficult at high levels of amorphous nylon copolymer. Beneficially, thesecond component (copolyamide) will be present in the blend in an amountof from about 10 to about 90 weight percent relative to the total weightof the blend. At amounts less than 10 percent and greater than 90percent, orientation of a film of the blend becomes increasinglydifficult, particularly for simultaneous biaxial orientation during adouble bubble type process. Also, use of amounts in excess of 90 percentreduces the beneficial optical properties of the blend. e.g. hazeincreases noticably. Optionally, a beneficial third component(homopolymer) may be present in the blend in an amount of from 10 toabout 30 weight percent. At amounts under 10 percent the beneficialeffect on physical properties such as oxygen barrier propertiesdecreases. Disadvantagely, amounts over 30 present increases stiffnessto undesirable levels for film processing. The above range of amountsand particular components and combinations are believed to provideenhanced processing and/or resin properties, and films made from suchresins show unexpected and surprising properties and results asdescribed below.

The present invention contemplates blown films as well as uniaxially orbiaxially oriented films of one or more layers. These thermoplasticflexible films may be made by well known conventional processes.

In multilayer film applications of the present inventions, the firstouter layer and second outer layer and additional optional intermediatelayers may be made of any suitable resins or resin blends. Nonlimitingexamples of suitable resins include polyolefin resins such aspolypropylene, low density polyethylene (LDPE), linear low densitypolyethylene (LLDPE), very low density polyethylene (VLDPE), andcopolymers and/or blends thereof including e.g. ethylene vinyl acetatecopolymer (EVA). Other examples of suitable resins include polyesters,other nylons, ionomers, poly (vinylidene chloride) copolymers (PVDC),ethylene vinyl alcohol copolymers (EVOH), and various blends thereof.

Preferred components of the outer layers are LLDPE, VLDPE, EVA andblends thereof. Linear low density polyethylene (LLDPE) refers tocopolymers of ethylene with one or more comonomers selected frompreferably C₄ to C₁₀ alpha-olefins such as butene-1, octene, in whichlong chains of copolymer are formed with relatively few side chainbranches or crosslinking. The degree of branching is less than thatfound in typical conventional low or medium density polyethylene. LLDPEmay also be characterized by the known low pressure, low temperatureprocesses used for their production. LLDPE is known to have a densitybetween about 0.91 and 0.93 grams per cubic centimeter and a meltingpoint of approximately 120° C. VLDPE is a copolymer of ethylene and atleast one comonomer selected from C₄ to C₁₀ alpha-olefins and having adensity between about 0.86 and 0.91 g/cc and a melting point of about120° C. EVA is a copolymer of ethylene and vinyl acetate. Preferred EVAresins will comprise between about 1 to 20 percent vinyl acetate byweight and most preferably 3 to 12 percent by weight. Advantageously,EVA may be blended with LLDPE or VLDPE.

Also, adhesives may be blended in the layers or adhesive layers may belaminated, coated or coextruded. Suitable adhesive resins includeanhydride based EVA and LLDPE resins. A preferred adhesive resin is anethylene based polymer containing vinyl acetate and anhydridefunctionality such as that sold by DuPont Company under the brand nameBynel CXA E-162.

For the blends, single and multilayer films of the present invention theresins utilized are generally commercially available in pellet form andas generally recognized in the art, may be blended by well known methodsusing commercially available blenders.

Also, if desired, well known additives such as processing aids, slipagents, antiblocking agents, pigments, and mixtures thereof may beincorporated into the film, generally in small amounts of up to about 10percent by weight by blending prior to extrusion.

The resins and any additives are introduced to an extruder (generallyone extruder per layer) where the resins are melt plastified by heatingand then transferred to an extrusion (or coextrusion) die for formationinto a tube. Extruder and die temperatures will generally depend uponthe particular resin or resin containing mixtures being processed andsuitable temperature ranges for commercially available resins aregenerally known in the art, or are provided in technical bulletins madeavailable by resin manufacturers. Processing temperatures may varydepending upon other process parameters chosen. In coextrusion, barreland die temperatures, for example, may range between about 175° C. and250° C. However, depending upon the manufacturing process used andparticular equipment and other process parameters utilized, variationsand actual process parameters including process temperatures will be setby one skilled in the art without undue experimentation.

In a preferred coextrusion type of double bubble process as described inU.S. Pat. No. 3,456,044 the primary tube leaving the die is inflated byadmission of air, cooled, collapsed, and then preferably oriented byreinflaring to form a secondary bubble with reheating to the film'sorientation (draw) temperature range. Machine direction (M.D.)orientation is produced by pulling e.g. by utilizing a pair of rollerstravelling at different speeds and transverse direction (T.D.)orientation is obtained by radial bubble expansion. The oriented film isset by cooling. Suitable machine direction and transverse directionstretch ratios are from about 1.5:1 to about 3.5:1 with a ratio of about2.5:1 preferred.

Oriented single layer films may also be made by the above process e.g.by extruding only a single layer or delamination. The orientation ofsingle or multilayer films may improve certain physical properties ofthe films as well as create films which are heat shrinkable. Also, thefilm may be stretched in the M.D. direction only, or stretchedsequentially (M.D. first followed by T.D. expansion) or simultaneouslystretched in machine and transverse directions.

Experimental results of the following examples are based on testssimilar to the following test methods unless noted otherwise.

Haze: ASTM D-1003-52

Gloss: ASTM D-2457, 45° Angle

Tensile Strength: ASTM D-882, method A

% Elongation: ASTM D-882, method A

1% Secant Modulus: ASTM D-882, method A

O₂ Transmission: ASTM D-3985-81

Elmendorf Tear Strength: ASTM D-1922

Gauge: ASTM D-2103

Shrinkage Values: Shrinkage value is defined to be values obtained bymeasuring unrestrained shrink at 90° C. for five seconds. Four testspecimens are cut from a given sample of the film to be tested. Thespecimens are cut to 10 cm. in the machine direction by 10 cm. in thetransverse direction. Each specimen is completely immersed for 5 secondsin a 90° C. water bath. The distance between the ends of the shrunkenspecimen is measured. The difference in the measured distance for theshrunken specimen and the original 10 cm. is multiplied by ten to obtainthe percent of shrinkage for the specimen. The shrinkage for the fourspecimens is averaged for the MD shrinkage value of the given filmsample, and the shrinkage for the four specimens is averaged for the TDshrinkage value.

Dynamic Puncture Resistance: Dynamic Puncture Resistance values aredefined to be those obtained by the following test. The dynamicpuncture-impact test procedure is used to compare films for theirresistance to bone puncture. It measures the energy required to puncturea test sample with a sharp pyramidal metal point made to simulate asharp bone end. A Dynamic Ball Burst Tester, Model No. 13-8, availablefrom Testing Machines, Inc., Amityville, Long Island, N.Y., is used, anda modified tip is installed on the tester probe arm for use in this testprocedure. The modified tip is constructed from a 3/8 inch diameterconical tip having a configuration of a right circular cone with theangle between the cone axis and an element of the conical surface at thevertex being about 65°. Three equally spaced and abutting planarsurfaces are machined to a smooth finish on the cone surface to form apyramidal shaped point. Six test specimens approximately 4 inches squareare prepared, a sample is placed in the sample holder, and the pendulumis released. The puncture energy reading is recorded. The test isrepeated until 6 samples have been evaluated. The results are calculatedin cm-kg per mil of film thickness and are averaged.

The following are examples and comparative examples given to illustratethe present invention.

In all the following examples, unless otherwise indicated herein thefilm compositions were produced generally utilizing the apparatus andmethod described in U.S. Pat. No. 3,456,044 (Pahlke) which describes acoextrusion type of double bubble method and in further accordance withthe detailed description above. All percentages are by weight unlessindicated otherwise.

EXAMPLES 1-2 AND COMPARATIVE EXAMPLES 3-4

The film compositions of Examples 1-4 were produced under similarconditions. For each example listed in Table 2 the components wereblended in the indicated weight ratio followed by heat plastificationand extrusion of a tube as generally described above and in theprocedure for making a single layer film as described in examples 7-13.Draw point temperature and bubble cooling rates were adjusted tomaximize bubble stability, and properties of each film are reported inTable 2. Examples 3 and 4 are comparative examples (not of theinvention) whereas examples 1 and 2 are of the present invention.

The films were extruded in the form of a seamless tube. The tubes werewound on cardboard reels and the end of each tube was secured by tape.Examples 1 and 2 represent identical films except that in the film ofExample 2 the reeled tube was then annealed in a circulating hot airoven at 100° F. to dimensionally stabilize the tube. During annealing,the tube flat width was reduced from about 6.25 inches to about 5 inchesby shrinkage.

Properties of an unannealed and annealed film of the present inventionare reported in Examples 1 and 2 respectively. The amorphous nyloncopolymer and copolyamide blend of Examples 1 and 2 formed a shrinkablefilm which was easy to orient with unexpectedly good optical propertiesincluding very high gloss and low haze relative to comparative examples3 and 4 which did not contain an amorphous nylon copolymer. Theunannealed film of example 1 had very high shrinkage relative to theunannealed comparative examples 3 and 4 (not of the invention).Annealing reduces the shrinkage as seen in example 2.

Also, the examples 1 and 2 of the invention demonstrated higher tensilestrength relative to the comparative examples 3 and 4 (not of theinvention).

A comparison of haze, gloss and tensile strength properties of theunannealed film of Example 1 with the annealed film of Example 2indicates that annealing may modify or improve some properties relativeto unannealed film. Moreover, both films (annealed and unannealed) ofthe present invention have improved tensile strength, superior gloss,and dramatically less haze than the unannealed comparative films. Ineach example and comparative example the amount of component A was heldthe same and component B was varied by substituting two differentcrystalline 6/12 polyamides for the amorphous polyamide of the presentinvention.

An annealed tube according to Example 2 of the present invention wasused as a sausage casing. This tube was hand stuffed with a beef andpork emulsion, and cooked. The resultant sausage casing had a good yieldwith uniform adhesion of the casing to the stuffed meat.

                                      TABLE 2                                     __________________________________________________________________________                                Tensile                                                                       Strength                                                                            Shrink                                                       A:B        × 10.sup.3                                                                    %                                           Nylon Blend Components                                                                         Wt. Haze   (psi) at 90° C.                            #   A     B      Ratio                                                                             %  Gloss                                                                             M.D./T.D.                                                                           M.D./T.D.                                   __________________________________________________________________________    1+  6/12 (CR9)                                                                          amorphous                                                                            4:1 2.1                                                                              93.1                                                                              23/23 51/49                                                 nylon                                                                         copolymer*                                                          2++ 6/12 (CR9)                                                                          amorphous                                                                            4:1 1.8                                                                              97.8                                                                              20/24 14/9                                                  nylon                                                                         copolymer*                                                          3   6/12 (CR9)                                                                          6/12 (CA6)                                                                           4:1 >30                                                                              13.3                                                                              15/15 19/22                                       4   6/12 (CR9)                                                                          6/12 (W6220)                                                                         4:1 >30                                                                               5.0                                                                              15/17 15/18                                       __________________________________________________________________________     *A nylon 6I/6T amorphous copolymer sold under the brand name Selar PA 342     was used.                                                                     +Unannealed film                                                              ++Annealed film                                                          

EXAMPLE 5 AND COMPARATIVE EXAMPLE 6

In Example 5 an amorphous nylon copolymer (nylon 6I/6T in the form ofSelar PA 3426) was added to the resin blend of comparative example 6(not of the invention). The blend of the invention (example 5) and thecomparative blend (example 6) were both processed under similarconditions into single layer films, (See the description for examples7-12 below) and similarly tested for tensile strength, tear strength,dynamic puncture resistance and shrinkage values. The test results asshown in Table 3 clearly demonstrate that addition of an amorphous nyloncopolymer such as 6I/6T to the substantially crystalline blend prior toprocessing produced a film with greatly increased tear strength andpuncture resistance. Tensile strength also showed improvement andshrinkage values were significantly higher.

The film of example 5 was used as a tubular seamless casing by firstannealing the tube at 100° F. as for Example 2 with a resultantreduction in flat width from about 6.25 inches to about 5.37 inches.Then the annealed tubular casing was hand stuffed with a meat emulsionand steam cooked at. 170° F. until the internal temperature reached 150°F. The resultant cooked, stuffed sausage had uniform adherence of thecasing to the sausage over the entire surface and at least as good of anappearance and cooking weight yield as a similarly made sausage having acommercially available nylon casing.

                                      TABLE 3                                     __________________________________________________________________________    Nylon Blend Components                                                                        Tensile                                                                             Elemendorf                                                              Strength                                                                            Tear  Dynamic                                                                              Shrink                                       nylon*                                                                            nylon**                                                                            nylon***                                                                           × 10.sup.3                                                                    Strength                                                                            Puncture                                                                             %                                            6/66                                                                              6/12 6I/6T                                                                              (psi) (gm/mil)                                                                            Resistance                                                                           at 90° C.                           # wt. %                                                                             wt. %                                                                              wt. %                                                                              M.D./T.D.                                                                           M.D./T.D.                                                                           (cm-Kg/mil)                                                                          M.D./T.D.                                  __________________________________________________________________________    5 72  18   10   27/21 49/76 2.3    35/32                                      6 75  25   --   22/24 15/16 1.6    22/25                                      __________________________________________________________________________     *The nylon 6/66 used was commercially available under the brand name Nylo     1539 from AlliedSignal Engineered Plastics of Morristown, New Jersey and      had a melting point of about 195° C.                                   **The nylon 6/12 used was commercially available under the brand name         Grilon W6220 from Emser Industries of Sumter, South Carolina and had a        melting point of about 135° C.                                         ***The amorphous nylon copolymer used was a nylon 6I/6T which was             commercially available under the brand name Selar PA 3426 from the DuPont     Company of Wilmington, Delaware and had a glass transition point of about     127° C.                                                           

EXAMPLES 7-13

Bioriented films of three and four component blends may be madeaccording to the present invention as demonstrated by the compositionsand properties of the films described in Examples 7-13. Blends of anamorphous nylon copolymer such as nylon 6I,6T and a crystallinecopolyamide having a melting point above 145° C. such as a commerciallyavailable nylon 6/12 (Grilon CR9) may be made with one or more othernylon 6/12 copolymers, nylon 6/66 copolymers or nylon homopolymers suchas nylon 6, nylon 11, and nylon 12.

Each single layer film was extruded and biaxially stretched (oriented)by a known double bubble extrusion process (See e.g. U.S. Pat. No.3,456,044). In forming the primary film tube, the resins wereconventionally blended and heat plastified in a conventional singlescrew extruder equipped with a standard commercially availablepolyethylene screw and conventional die similar to the proceduredescribed for examples 12-21. The extruder barrel temperature rangedfrom 350° F. to about 450° F. and the die temperature was set at about435° F. The machine direction (M.D.) orientation ratio was from about 2to 2.5 and the transverse direction (T.D.) orientation ratio was fromabout 2 to 3. In order to minimize equipment changes during experimentalruns and provide physical support and reduce adhesion to equipment eachsingle layer film was formed by coextrusion of the nylon containinglayer with a polyethylene layer such as linear low density polyethyleneto form a primary tube. The polyethylene outer layer was then strippedoff after cooling of the primary tube but prior to biaxial orientationto yield a single layer film. It is expected that single layer films maybe conventionally formed by one of ordinary skill in the art withoutneed for coextrusion of a second layer.

Single layer films having various nylon blend components are listed inTable 4 as Examples 7-13. In all of these examples the blends producedbioriented films having good shrink properties in both the machinedirection and the transverse direction. In examples 9 and 11, shrinkagewas determined to be comparable to the other examples in Table 4,however, shrinkage measurements were made of the fresh film soon afterorientation whereas measurements of examples 7, 8, 10, 12 and 13 weremade several days following orientation.

The optional addition of nylon homopolymers may improve gas barrierproperties by lowering permeability. In examples 11 and 13, the nylon 6and nylon 12 polymers, were commercially available nylon homopolymerssold under the respective brand names Emser F40 (nylon 6) and Emser L25(nylon 12) by Emser Industries of Sumter, S.C. In example 12, the nylon11 polymer was a nylon homopolymer commercially available under thetrade name Rilsan Besno nylon 11 from Rilsan Corporation of Glen Rock,N.J. Surprisingly, as shown in example 12, addition of nylon 11 whichhas a relatively high O₂ permeability (28cc mil/24 hrs/100 in² /1 arm)yielded a film with a lower oxygen permeability (relative to examples 7and 8 which did not contain a homopolymer such as nylon 11).

                                      TABLE 4                                     __________________________________________________________________________    Nylon Blend Components                                                                Nylon                     SHRINK                                                                              O.sub.2 TRANS.                        Amorphous                                                                             6/12**  Nylon             %     cc mil/                               Nylon*  m.p. > 145° C.                                                                 6/12***                                                                            Other Nylon  at 90° C.                                                                    100 in.sup.2 /                        # wt. % wt. %   wt. %         wt. %                                                                             M.D./T.D.                                                                           24 hr/1 atm                           __________________________________________________________________________     7                                                                              10    72      18                32/26 5.45                                   8                                                                              20    72      8                 48/46 4.79                                   9                                                                              18    57.6    14.4 nylon 6/66.sup.+                                                                       10  N.D.  N.D.                                  10                                                                              18    57.6    14.4 nylon 6/12.sup.++                                                                      10  40/43 2.33                                  11                                                                              18    57.6    14.4 nylon 6.sup.+++                                                                        10  N.D.  N.D.                                  12                                                                              18    57.6    14.4 nylon 11.sup.++++                                                                      10  35/38 1.46                                  13                                                                              18    57.6    14.4 nylon 12.sup.+++++                                                                     10  38/38 1.76                                  __________________________________________________________________________     N.D. -- Not Determined                                                        *An amorphous nylon 6I/6T copolymer commercially available as Selar PA        3426 (trademark of E.I. DuPont de Nemours & Co.).                             **A nylon copolyamide of nylon 6/12 commercially available as Grilon CR9      (trademark of Emser Industries).                                              ***A nylon copolyamide of nylon 6/12 commercially available as Grilon         W6220 (trademark of Emser Industries).                                        .sup.+ Nylon 1539 (trademark of AlliedSignal Engineered Plastics).            .sup.++ Zytel 151 (trademark of E.I. DuPont de Neumours & Co.).               .sup.+++ Emser F40 (trademark of Emser Industries).                           .sup.++++ Rilsan Besno (trademark of Rilsan Corporation).                     .sup.+++++ Emser L25 (trademark of Emser Industries).                    

EXAMPLES 14-24

A series of multilayer films according to the present invention weremade by the above described coextrusion type of double bubble processwith a nylon blend intermediate layer. The physical properties of thesemultilayer films and two comparative examples were tested and theresults are listed as examples 14-24 in Table 5. Comparative examples 14and 15 are not of the present invention whereas the remaining examplesare of the present invention.

Each multilayer film was coextruded and biaxially oriented by knowncoextrusion and orientation processes (see e.g. U.S. Pat. No.3,456,044). For the three layer films of examples 16-24 a layerthickness ratio of 12:7:6 was used which corresponds to first outerlayer: intermediate layer: second outer layer, respectively. The layerratio of example 14 was 2:1:2. In forming the blown film tube, the firstouter layer, corresponds to the outermost layer of the tube and thesecond outer layer corresponds to the innermost layer of the tube. Threesingle screw extruders equipped with polyethylene metering screws wereutilized with the extruders attached to a conventional coextrusion die.The die diameter was 1.25 inches. The extruder barrel temperature rangedfrom about 350° to about 450° F. with the die temperature set at about435° F. The machine direction orientation ratio was from about 3:1 to5:1 and transverse direction orientation ratio was from 3:1 to 5:1. Theresins of examples 14-24 were coextruded and bioriented according toknown methods as outlined above and the resultant oriented films tested.

Examples 16, 19-23 are three layer films in which both outer layers ofeach film comprise a copolymer of ethylene with vinyl acetate (EVA).Each outer layer was blended with 10% by weight (relative to the weightof the outer layer) of an adhesive resin (Bynel 162-E). This adhesivewas also blended in like amount with the very low density polyethylene(VLDPE) which comprised both outer layers of examples 18 and 24 as wellas the second outer layer of example 17. The first outer layer ofexample 17 was an EVA blended with an adhesive similar to the other EVAlayers in this group of examples.

Both outer layers of comparative example 14 comprised a linear lowdensity polyethylene (LLDPE), whereas both outer layers of comparativeexample 15 comprised VLDPE. Comparative example 15 suffered fromdelamination and both outer layers were removed after orientation.Therefore, the test results for example 15 are for the intermediatelayer of nylon 6/12 copolymer alone.

Examples 14-24 were nested for tensile strength, ultimate elongation,secant modulus at 1%, shrinkability at 90° C., dynamic punctureresistance, haze, gloss and oxygen gas transmission. The results ofthese tests are listed in tabular form in Table 5 along with the averagegauge of the test sample, and composition of the films.

Example 14 (not of the invention) contained a 100% amorphous nylonintermediate layer. It did not contain any copolyamide having a meltingpoint greater than 145° C. as required by the present invention. Thefilm of example 14 was difficult to process and orient relative to filmsof the instant invention. Also, the biaxially oriented film ofcomparative example 14 has a very low shrinkage value (less than 5%).Also, the film of example 14 has comparatively low gloss and high haze.However, the film of example 14 does have excellent oxygen barrierproperties and tensile strength. This film is the subject of a U.S.patent application Ser. No. 091,172, the disclosure of which is herebyincorporated by reference in its entirety.

Comparative example 15 (not of the invention) contained an intermediatelayer having 100% by weight of a copolyamide having a melting pointgreater than 145° C. The test results are of the intermediate layeralone, but do not indicate or suggest the surprisingly good physicalproperties of the present invention as shown in Table 5 and discussedbelow.

Examples 16-24 of the present invention demonstrate that biaxiallyoriented multilayer films having a nylon blend intermediate layer withmultilayer film shrinkage values of 5% or greater may be made accordingto the present invention. Advantageously, multilayer films withshrinkage values of 20% or higher in one or more directions may beproduced with shrinkage value greater than 40% obtainable for variousfilm compositions.

All of the examples of the invention having both outer layers of EVAshow excellent optical properties with very high gloss and very lowhaze. Increasing the proportion of the amorphous nylon in the blend, asseen in examples 19-23, exhibits a corresponding increase in 1% secantmodulus values and a corresponding decrease in ultimate elongationpercentages and transmission of oxygen across the film.

A comparison of inventive examples 16-24 shows that shrinkability of thefilms may be adjusted either by variation of the amount of amorphousnylon is the blend or by changing the composition of one or more of theadded layers. All the films of the present invention exhibit goodtensile strength and relatively good oxygen barrier properties for nylonfilms.

The results shown in Table 5 demonstrate that biaxially orientedcoextruded multilayer films having a novel nylon blend as anintermediate layer can be successfully made with useful properties andthat the properties of these films can be adjusted either by changingthe composition of the nylon blend or by varying the type of layer towhich the nylon layer is attached.

                                      TABLE 5                                     __________________________________________________________________________    NYLON BLEND                        TENSILE                                    INTERMEDIATE                       STRENGTH                                   LAYER             FIRST SECOND                                                                              AVG. × 10.sup.3                                                                     ELONG.                                 A++ B+++ C++++ OUTER OUTER GAUGE                                                                              (psi)  %                                   #  wt. %                                                                             wt. %                                                                              wt. % LAYER+                                                                              Layer+                                                                              (mil)                                                                              M.D./T.D.                                                                            M.D./T.D.                           __________________________________________________________________________    14 100  0    0    LLDPE LLDPE 2.7  27/27  78/26                               15*                                                                               0  100   0    VLDPE VLDPE .5   21/27  42/76                               16 20  72    8    EVA   EVA   2.4  7.1/9.6                                                                              182/210                             17 20  72    8    EVA   VLDPE 2.9  9.7/7.9                                                                              240/416                             18 20  72    8    VLDPE VLDPE 3.6  7.9/9.8                                                                              251/247                             19 20  64   16    EVA   EVA   2.3  11.5/9.6                                                                             158/247                             20 30  56   14    EVA   EVA   2.7  12.5/9.5                                                                             141/254                             21 40  48   12    EVA   EVA   2.3  9.3/9.5                                                                               91/152                             22 50  40   10    EVA   EVA   2.1  10.2/8.4                                                                              91/124                             23 70  24    6    EVA   EVA   2.3  8.6/5.4                                                                              70/70                               24 50  40   10    VLDPE VLDPE 1.4  9.8/9.3                                                                              113/175                             __________________________________________________________________________                SECANT                                                                        MODULUS                                                                       at 1%  SHRINK                O.sub.2 TRANS.                                   × 10.sup.3                                                                     AT 90° C.                                                                    DYN.            (cc mil/                                         (psi)  %     PUNC.  HAZE     100 in.sup.2 /                                #  M.D./T.D.                                                                            M.D./T.D.                                                                           (CmKg/mil)                                                                           %   GLOSS                                                                              24 hr/atm)                           __________________________________________________________________________             14  80/111                                                                              3/2   <.5    >30 18   6.8                                           15*                                                                              N.D.   27/34 <.5    10  39   N.D.                                          16 27/14  37/35 2.4     3  74   13.44                                         17 11/39  32/27 2.5    15  40   19.0                                          18 22/19  30/22 3.0    25  28   20.0                                          19 24/22  47/44 3.6     3  78   20.2                                          20 25/23  49/41 3.2     3  79   12.8                                          21 28/32  40/43 3.4     4  74   11.3                                          22 41/33  23/24 2.7     6  70   9.9                                           23 95/58  26/19 2.5     6  67   7.5                                           24 37/72  16/25 3.1    28  24   10.0                                 __________________________________________________________________________     N.D. = Not Determined                                                         +Outer layers of examples 16-24 included 10% by weight of Bynel 162E          (trademark of E.I. DuPont deNemours & Co., Wilmington, DE) which is a         commercially available ethylene based polymer adhesive resin containing       vinyl acetate and anhydride functionality.                                    ++Amorphous nylon copolymer nylon 6I/6T sold under trademark Selar PA 342     by DuPont).                                                                   +++Nylon 6/12 copolyamide having m.p. > 145° C. (sold under            trademark Grilon CR9 by Emser Industries, Sumter, SC).                        ++++Nylon 6/12 copolyamide having m.p. < 145° C. (sold under           trademark Grilon W6220 by Emser Industries, Sumter, SC).                      *Test results are for the nylon intermediate layer only. The outer layers     of VLDPE were removed prior to testing.                                  

Although one and three layer film embodiments of the present inventionhave been described above, these examples, are merely illustrative andtwo layer as well as four or more layer films are contemplated. Thesemultilayer films may be formed by any method known in the art includingboth coextrusion and lamination processes as well as combinedcoextrusion and lamination. In particular, it will be appreciated by oneof skill in the art in view of the present disclosure that additionalintermediate layers may be provided as desired to achieve additionalbeneficial or optimum properties or meet performance requirements. Theseadditional intermediate layers need not contain nylon. For example,adhesive layers may be provided or other layers added which provideimproved puncture resistance, strength, shrink force, or additionalbarrier properties. Similarly, outer layers may be formed of a varietyof resins or blends e.g. to enhance heat sealability, printability,puncture resistance, or to provide additional barrier properties.

Beneficially, in food packaging applications such as for meat orpoultry, a thermoplastic film or film layer comprising an amorphousnylon copolymer and copolyamide blend according to the present inventionwill preferably range in thickness from about 0.3 to about 1.5 mils.Thinner and thicker films, while still of the invention, become weakeror more costly, respectively. Generally, in these food packagingapplications, multilayer films having sufficient desired propertiesincluding strength will be in the range of 1.5 to 3.5 mils.

In a preferred multilayer food packaging embodiment, the multilayer filmstructure utilizes an intermediate layer containing an amorphous nyloncopolymer and copolyamide blend which acts as an oxygen barrier layerand comprises about 20 to about 30 percent of the total thickness of themultilayer film. The outer layer adapted for placement adjacent to afood product is generally about 45 to about 55 percent of the totalthickness and the opposing outer layer is typically 20 to 35 percent.Generally, in poultry and meat food packaging applications, the outerlayer closest to the packaged product must have sufficient thickness toensure heat sealing integrity: the intermediate barrier layer must besufficiently thick to provide its gas barrier properties at desiredlevels; and the outer layer adapted for placement opposite the packagedproducts must have sufficient thickness to withstand handling and otherexternal forces. However, it is contemplated that those of ordinaryskill in the art will readily vary layer and film thicknesses accordingto particular packaging requirements. Generally, in commercial packagingfor cook-in and processed meat applications, films (including multilayerfilms) desirably have an oxygen permeability value of less than about4.5 cc/100 in.² in 24 hours at 1 atmosphere as measured by ASTM0-3985-81 in order to protect meat from deterioration due to exposure tooxygen.

It is further believed that properties such as high temperature punctureresistance of the inventive single and multilayer films, may be improvedby irradiation and/or crosslinking according to known methods.Preferably, the entire film is irradiated after orientation.Alternatively, one or more single layers may be oriented and irradiatedand optionally formed into a multilayer film by lamination processeswith other irradiated or nonirradiated layers. A suitable irradiationdosage is irradiation up to 10 Mrad with irradiation from 1 to 5 Mradpreferred. Known irradiation procedures may be utilized. Variousprocedures are described in U.S. Pat. No. 4,044,187.

The multilayer film of this invention is preferably produced by acoextrusion type of double bubble method. The extruder screws and diesused in the examples were standard polyethylene screws and 11/4" dies.These screws and dies were suitable to make films of the presentinvention. However special screws for use with polyamide (nylon) resinsare commercially available and may provide enhanced performance as mayother commercially available dies. The multilayer film may also befabricated by extrusion coating, wherein a base tube is extruded andsucceeding layers are surface coated on the base tube in a manner suchas that disclosed in U.S. Pat. No. 3,741,253. Also, single or multilayerfilms may be slot cast and uniaxially or biaxially stretched bytentering. Still further, the inventive multilayer film may befabricated by producing separate film layers and then laminating thelayers together or by a lamination biaxial orientation type of doublebubble method.

The multilayer film of the invention may be wound up as flattened,seamless, tubular film to be used later to make bags. Bags having endseals are typically made by transverse heat sealing across the width offlattened tubing followed by severing the tubing so that the transverseseal forms the bag bottom. Alternatively, side-seal bags may be formedin which the transverse seals form the bag sides and one edge of thetubing forms the bag bottom.

Various conventional additives such as processing aids slip agents,anti-block agents, plasticizers and pigments can be incorporated intosingle and multilayer films of this invention, as is well-known in theart.

The above examples serve only to illustrate the invention and itsadvantages, and they should not be interpreted as limiting since furthermodifications of the disclosed invention will be apparent to thoseskilled in the art. All such modifications are deemed to be within thescope of the invention as defined by the following claims.

What is claimed is:
 1. A nylon resin blend comprising a blend of: (a) anamorphous nylon copolymer consisting of hexamethyleneisophthalamide-hexamethylene terephthalamide units and having nomeasurable melting point (less than 0.5 calories per gram) or no heat offusion, as measured by differential scanning calorimetry, which ispresent in an amount of from about 10 to about 50 weight percent of saidblend, and(b) a nylon 6/12 or nylon 6/66 copolyamide having a meltingpoint of at least 145° C.
 2. A nylon resin blend, as defined in claim 1,wherein said copolyamide has a melting point within a range of fromabout 145° C. to about 215° C.
 3. A nylon resin blend, as defined inclaim 1, wherein said copolyamide having a melting point of at least145° C. is present in an amount of from about 24 to about 90 weightpercent.
 4. A nylon resin blend, as defined in claim 1, furthercomprising a polyamide homopolymer in said blend.
 5. A nylon resinblend, as defined in claim 1, wherein said copolymer has from about 65to about 80 percent of its polymer units derived fromhexamethyleneisophthalamide.
 6. A nylon resin blend, as defined in claim4, wherein said polyamide homopolymer is present in an amount of fromabout 10 to about 30 weight percent.
 7. A nylon resin blend, as definedin claim 4, wherein said polyamide homopolymer comprises nylon
 11. 8. Anylon resin blend, as defined in claim 7, wherein said copolyamide isnylon 6/12.
 9. A nylon resin blend, as defined in claim 7, wherein saidcopolyamide is nylon 6/66.
 10. A thermoplastic flexible film comprisinga blend of:(a) an amorphous nylon copolymer consisting of hexamethyleneisophthalamide-hexamethylene terephthalamide units and having nomeasurable melting point (less than 0.5 calories per gram) or no heat offusion, as measured by differential scanning calorimetry, which ispresent in an amount of from about 10 to about 50 weight percent of saidblend, and (b) a nylon 6/12 or nylon 6/66 copolyamide having a meltingpoint of at least 145° C.
 11. A thermoplastic flexible film, as definedin claim 10, wherein said copolyamide has a melting point within a rangeof from about 145° C. to about 215° C.
 12. A thermoplastic flexiblefilm, as defined in claim 10, wherein said copolyamide is a copolymer ofnylon 6 and nylon
 12. 13. A thermoplastic flexible film, as defined inclaim 10, wherein said copolyamide is a copolymer of nylon 6 and nylon66.
 14. A thermoplastic flexible film, as defined in claim 10, furthercomprising a polyamide homopolymer in said blend.
 15. A thermoplasticflexible film, as defined in claim 10, wherein said copolyamide having amelting point of at least 145° C. is present in an amount of from about10 to about 90 weight percent.
 16. A thermoplastic flexible film, asdefined in claim 14, wherein said polyamide homopolymer is present in anamount of from about 10.to about 30 weight percent.
 17. A thermoplasticflexible film, as defined in claim 14, wherein said homopolymercomprises nylon
 6. 18. A thermoplastic flexible film, as defined inclaim 14, wherein said homopolymer comprises nylon
 11. 19. Athermoplastic flexible film, as defined in claim 14, wherein saidhomopolymer comprises nylon
 12. 20. A thermoplastic flexible film, asdefined in claim 10, wherein said copolymer has from about 65% to about80% of its polymer units derived from hexamethyleneisophthalamide.